Reservoir sampling



Jan., 7, 1958 5. E. EGKEL RESERVOIR SAMPLING E. Sheets-Sheet LL Filed Jan. 14, 1955 4 537, H .4 444 .DU f E Inventor Jan. 7, 1958 J. E. ECKEL RESERVOIR SAMPLING Filed Jan. 1.4, 1955 2 Sheets-Sheet 2 III lai TUBING STRING TUBING STRING Im 4 www L T LAL AVA OR AVHP ME o l S Tl U lV A S A H B V X ...VES G R I OLEZW O U AIR MOTOR AIR TUBE TO AIR JET PACKER HIP BASKET CHIPPING BI FIG. 2

Inventor John E. Eckel BI/gw AHorney United St RESERVOIR SAMPLING ohn E. Eckel, Tulsa, Okla., assignor to Esso Research and Engineering Company, a corporation of Delaware The present invention concerns means for obtaining an lncontaminated sample from a subterranean formation. t particularly relates to a method and apparatus for obaining an uncontaminated sample of a petroliferous fornation at the bottom of a bore hole or well which penerates the formation. The method and apparatus are )articularly characterized by the fact that the formation :ample is obtained without employing drilling mud, the presence of which has been found to seriously contam- ,nate such samples. The method and apparatus are urther particularly characterized by the fact that the formation sample is continuously maintained under sub stantially ambient formation pressure.

A serious and important problem that confronts the petroleum producing industry at the present time is one of obtaining reliable samples of petroliferous formations that lie beneath the surface of the earth. The problem has become one of particular importance in view of the ever increasing use of secondary recovery methods for obtaining additional oil from subterranean oil reservoirs that have ceased primary production. it is essential, before initiating a secondary recovery procedure in any such reservoir, to have as much information as possible about the structure, the iiuid content, the pore volume, the permeability, etc. of the formation. Such information is extremely valuable in determining whether the formation is susceptible to Successful exploitation using secondary recovery techniques and which techniques should preferentially be utilized.

ln line with 'the growing emphasis on secondary recovery programs, many petroleum producers are conducting extensive analyses of old reservoirs and elds that have in years past lost their reservoir pressure and been abandoned. In an effort to evaluate these old reservoirs and fields and in order to determine whether a secondary recovery procedure can be successfully applied to them, the producers are conducting extensive sampling programs. One sampling technique has been to drill and sample the bottoms or side walls of old wells that were originally producing weils associated with the reservoirs or fields. lt has been determined, however, that the samples derived by this technique are quite inaccurate and not representative of the eld or reservoir as a whole. Accordingly, it has become more and more the established practice to drill entirely new holes from the earths surface down to any given petroliferous forma tion and to obtain samples of the formation directly from these new holes. Conventional drilling and` coring methods such as rotary and cable tool have been employed for this purpose. Another frequently used method employs an electric motor suspended in the well by an electrical conductor cable which in turn operates a circulating pump and conventional rotary core barrel. This requires only enough liquid in the hole bottom to permit circulation by the pump. In all of these types of drilling, however, it is necessary to use at least a small amount of drilling mud, water or other drilling uid in the bottom of the hole in order to properly lubricate 'the bit tes Patent i' '2,819,038 lPatented Jan. 7, 1958 and to dispose of the cuttings; and it is therefore conventional to have at least about 25 to 50 feet of water or other drilling fluid within a hole.

The presence of the drilling mud, water or other drilling liquid in a hole still constitutes an undesirable feature when sampling a reservoir of the type described above for the reason that the hydrostatic pressure and wetting effects of even this small amount of liquid are considered to seriously interfere with the reliability of the samples that are obtained. It is accordingly an objective of the present invention to provide an apparatus and method for obtaining reservoir samples wherein the samples are not subjected to a drilling liquid of any kind. lt is a further object of the invention to provide means for sampling a formation in such a manner that the sample suffers a very limited exposure to any material that could conceivably be a source of contamination. It is a further objective of the invention to provide means for obtaining and retaining the sample under substantially ambient formation conditions.

These objectives are realized in accordance with the in vention by utilizing a pneumatically powered percussiontype of bit to cut into the formation at the bottom of a bore hole. The pneumatic power unit and the associated bit may be suspended Within the bore hole at the bottom of a conventional string of drill pipe which in turn may serve as a conduit for the passage of compressed air from the earths surface to the power unit. The exhaust air from the unit is vented directly up the annular space between the drill string and the wall of the bore hole.

An additional amount of air is directed vertically downward and in proximity to the drill bit in order to cool the bit as well as the sample that is cut by the bit. The air that is directed downward in this manner also serves to blow the drill cuttings from the bottom of the bore hole upward within the annular space between the overall apparatus and the wall of the bore hole. ln this way the air serves as a drilling iluid and keeps the bottom of the bore hole clear of cuttings.

At least a portion of the rock chips that are cut from the bottom of a bore hole by the present apparatus is removed from all contact with` the air substantially as soon as it is cut. This precaution prevents the: sample from losing any of its fluid content due to prolonged contact with the air. Once the sample has been separated from the air stream, it is then retained under substantially the same conditions of pressure that prevail within the formation. Thus, the invention provides samples of subterranean formations that are substantially uncontaminated and that are truly representative of the formations.

The above described features of the invention may be better understood by reference to the lattached figures which illustrate different embodiments of the invention.

Figure l is a vertical, partially sectioned view of a particular embodiment of the invention wherein the sample is collected in a container located in the annular space between the drilling apparatus and the wall of the bore hole.

Figure 2 is a modified form of Figure l in which a packer to seal samples in the chamber is illustrated in `the deliated form.

Figure 3 is identical to Figure 2 but with the inated packer sealing the sample in the chamber.

Figure 4 is a modied form of the upper portion of the devices shown in Figures l3 with a pressure inflated packer and suitable orifices added to maintain controlled pressures in the vicinity of the bit during the drilling and sample collecting process.

Turning tirst to Figure l, there is illustrated in this iigure an apparatus that includes a tubing string 6, and air motor 7, a percussion-type bit 8, a chip basket 9 and an air jet lll. The apparatus is depicted as drilling a hole l1 within a formation 12.' The bit 8 is driven in a reciprocating up and `do"wn action by the motor 7 itlrroughthe reciprocating shaft 13.

The air motor 7 may be any ,conventional type of reciprocating, pneumatic, motori-e. g. Jan ,air' hammerwhich is` adapted to provide a vertical reciprocating ac:4 tion to the shaft 13.v The motorlor hammer is'actuated bycompressed air, whiclrreaches itfr'om the" earths surface by means of tubing string The air exhausted from-' the motor is directed through the exhaust pipe f4' and isI then vented 'directly to the earths surface through the.

annular space 16 between the tubing string 6 and the' wall of the` bore holellx" An additional amount-of air is conducted to the bottom of the bore .hole VAand is directed. toward and .in the vicinity of the bit.8.' It'willbe'notedthat tube l5 'in extending to thebottonr ofthe bore hole' passes throughjthe chip basket 9,. Where the tube pierces thisbaskea'a tight This feature is readily/at-A tained by constructing the basket to have an annularcon-lv formation around 'the outer periphery of vthe shaft: In

other words, the basket isbuilt withan outer cylindrical wall'l' and an inner cylindrical wall 18,'both of which are sealed around 'their -bottom peripheriesto' a lower` end member .19." The inner .Wall18 'extends vertically upward to and is sealed to the air motor 7; and a beare ing inthe end member 19jis`provided topermit movement of the shaft 13 relative to the basket 9." The bearing Ztl'may further be provided with 'a suitable O-ring,Y

stufng ybox or other packingrmeans for preventing airand/or solid particlesfrom entering the annularY space "bef tween the shaft 13 and the inner wall '18.1

Drill 'bit 8 may be of any conventionaljhardened steelv type that is used in cutting throughfrock .formations and thelike. A bit that is contemplated to' be kparticularly effective in the apparatus of the ligure isa'star-type drill bit. As illustrated, the drill bit is flush against thebot-4` tom Vof the bore holej at the endiof the stroke imposed upon it by the pneumatic motor 7. Dotted-linesare-"alsoA shown in the iigure toindicate where' the' bit `is positioned at the other end of the motor stroke: The: overall lstroke may conveniently be from Mt' inch to' 6 inches, `and'v itis contemplated that .a stroke of about 2 'inches is .preferred in the greatest number of instances.

The preceding paragraphs have been devoted largely to a discussion of the structural details, of'the'apparatus in Figure l.

the best manner of 'operating thel apparatus infthe ligure. that bore holelll has been drilled in a conventional'man'- ner and that any drillingmud or'other"drillingriluidy has been removed from thehole. that the hole,.if'it1is an old one, ris substantiallyy dry and free of any liquid.

that the bit'is positioned roughly' as shown so' that it These and other details" are better'under-v stood by brieliy considering what is contemplated to'bek In'presenting such a discussion, it i's'iirstassumed-4 It may also be assumed It is 'further-assumed:l that^thc drill has been loweredwithin the hole for operation and' strikes, the .bottom of 'the hole on the4 down "stroke of" the: motor 7.

With these conditions in mind the apparatus' is started by passing compressed air from a compressor or other source of high pressure air located on theiearths 'surface down throughthe tubing7 .string 6 to thel air motor 7 'and theconduit l5;A The amount'ofairsent-'to the motor. mustbe suflicient to Adrive the` bit 8 vagainst the* bore hole bottom and to fracture the underlying forma- 4 tion into small chips. The amount of air that is sent through'fthe conduiti Mirl-turn is y-gove1ned"by( l the amount of cooling that must'fbe realized in the vicinity of the drill bit and (2) the amount of air required to blow cuttings from the bottom of the bore hole up and above the chip basket 9. In this connection it is contemplated that the chips may range in particle size from about Mt inch to 11/2 inchesand'th'at air velocities within the range of aboutit() 'to lOftper. secondy are required to suspend and pass these chips upward within the bore hole; Once fthe chips'pass"the'ammlar Aspaceibetween`4 the chip basket 9 vand the' wall ofthe' bore"hole;" the velocity of the chips-and airis greatly reduced dueto the increased volume afforded bythe annular settling chamber 45 between theinnerwallf13 `'of'rthe ychip basket 9 and the wall of the bore hole. This reduction in velocity causes the chips to be disengaged from the air stream and to drop within the chip basket. It will be noted that' it'maybe desirable insome instances torprovide settling the chips'fromthe air' stream' into the basket.A These screens; deflectorsorthe'like 'may be 'supported yin lanyl convenientmanner as -by--connectingthem-to theinner contemplated that samplesof about-300'lbssbe provided for. Whenv the'desired'arnount of sample has been taken;

the-flow of'compressed air may' lne-stopped and the'en tire apparatus-withdrawn fromI the holes' At thispoint it -is Well'to note thata number'of modi-vr fcationsv may be -made to the --apparatu`s `Aof Figurel l Without -departing from ythe spirit 4orscope of the inven-y tion. Thus, it may be desirable on occasions'to 'case and cement the borehole 16 in vorder to-v obtain more satisfactoryoperation: andv results. f Furthermoreg-the size ofthe chip basket,-the size of lthey chips, the'velocity of -the air, etc. may-be modified as desired toy suitthe 1 particular type offormation'being drilled.'V

Attention is nowdirected toward FiguresZ andl 3 which illustrate a preferred embodiment of the invention;y Thel apparatus in these iigures includesall of-"the critical features illustrated in the apparatus 'of Figure "l and in` addition provides means forisealing the 'chip' collecting basket 9.' Thus, the apparatusrin Figure'Z 'includes'a percussion bitS, a chip basket 9, an air `motor'7, a tub#V ing Vor drill string 6 and furthermore includes a packer 38, a sleeve valve 40` and a packerconduit 39. The packer 38' may be mountedv on the inner wall portionl 18 ofthe chip basket9 and upon inflation extends `outwardlyl to and engages the outer wall `17v ofthe basket;` The packer itself mayv be constructedof the usual elasticand deformable materials that are employed in inflatable packers;

As illustrated in Figure 2, packer 38 is connected to drill string 6 andl air is suppliedv thereinby means of an interconnecting packer conduit 39. At thepupper end of conduit39, (where this conduitenterstheLdrillstringi) there is :providedsleeve valve 40 which normally'is posi; tioned laterally oppositetheconduit the same from airinthe drill string.

is maintained in this normal position throughout a drilling and sampling operation'. When-these operations have been completed,l however, air is admitted to thepacker 38 whereby the packerisinflated as Vin'Figurel ,3 and the basket 9 thereby kcompletely sealed. The admission of the air to the packer is realized by merely dropping a go-devil ,operating plug, the idrill string 6 and against the top` of the valveV 40; The' godevil forces the sleeve valve 401:0` move in 'a down-1 ward ldirection against spring 42 thereby uncovering the chamber 45 withporous screens ortdeilectorstli above the lchipv basket `inorder'to more positivelydirect the settling chamber.' i' should be of-a lengthandvolume 1 39 thereby sealing The sleevevalve;A

Vor other suitabl`e wcight .down

asignan entrance conduit 39 and directing air through that conduit into the packer 38. This action is particularly well illustrated in Figure 3 where a valve operating plug 41 is depicted as having forced valve 40 down against spring 42 thereby opening conduit 39 to a flow of air from drill string 6.

Once packer 38 has been expanded and basket 9 thereby sealed, the supply of air to the drill pipe may be cut oi and the pressure in the drill pipe lowered essentially to atmospheric pressure without breaking the seal on the basket 9. The maintenance of the basket seal may be achieved by selection of a spring 42 which is adapted to close the sleeve valve 40 when the pressure in the drill string has been lowered but before the packer 38 has become deflated. Alternatively and preferably, the seal may be maintained by providing a small check valve 48 within conduit 39 which is adapted to permit the flow of air into the packer but to prevent any back flow of air from the packer. In either case, once the packer has been expanded and sealed against the outer wall of the chip basket, the basket may be safely raised to the earths sur face without contamination of the sample in the basket.

In those instances where it is desirable to make sure that the sample which is collected in the chip basket of the apparatus hereinbefore described is under at least the same pressure as the surrounding formation, additional apparatus features of a type shown in Figure 4 may be utilized. Turning to Figure 4, there is illustrated a packer assembly 46 which is located above the air motor 7-corresponding to the air motors in Figures l to 3 and which surrounds and is supported by the drill string 6. Packer assembly 46 includes a balloon-type packer 43, a conduit member and a variable choke orifice 44. The conduit 45 extends vertically from one end of the packer assembly 46 to the opposite end and is essentially a vent connection providing for the llow of air from a point beneath the packer to a point above the packer. The interior of the packer itself is connected directly to the interior of the drill string 6 by one or more passageways 47. Conduit 14 carrying the exhaust air from air motor 7 passes directly through packer assembly 46 and is adapted to vent exhausted air from the air motor to a point above the packer assembly.

The packer assembly 46 in Figure 4 insures that the chip samples formed and collected by the apparatus of Figures l to 3 are maintained under at least formation pressure in the following manner. Air passing down through drill string 6 flows through passageways 47 into the interior of balloon packer 43 thereby inating this packer and creating a seal against the inner surface of the bore hole. This seal thus separates the portion of the bore hole beneath the packer from the portion above the packer.

Air to the motor 7 ows as before through drill string 6 directly to the motor and is then exhausted to the atmosphere through vent conduit 14. The air that is jetted through conduit 15 to the bottom of the bore hole, however, upon cooling the drill bit and upon lifting the drill cuttings into the sample basket, now must ow through conduit 45 and orifice 44 before it vents to the atmosphere. Thus, by selecting or adjusting the size of the orifice 44, it is possible to maintain a pressure below the packer assembly 46 which is at least equal to the pressure in the surrounding formation. The control of the pressure below the packer assembly may be further aided by the use of an additional orice not illustrated which is provided in the air jet at the bottom of the bore hole.

It will be noted in Figure 4 that the pressure within the drill string 6 and the balloon packer 43 has been desig-Y nated as P1, while the pressures below and above the packer assembly are designated as P2 and P3 respectively. The pressure of the formation has also been identified by a character PF. With these legends in mind, it is particularly contemplated that the apparatus in Figure 4 be operated such that P1 is greater than P2 and P2 is greater than both PF and P3. By employing these pressure differentials, the sample obtained by the apparatus is protected against the loss of any fluids.

In `operating the apparatus in Figures 1-4, it is contemplated that percussions of about 50 to 300 per second should be imparted to the core bit. The precise number may vary somewhat within that range depending upon the type of formation encountered in any given case. It is further contemplated that the bore hole may be of any desired size, as for example, from about 5 to 10 inches in diameter. In most instances it is preferred that the bore hole diameter be about 8 inches in size. During the drilling operation tubing 6 may be rotated slowly from the surface to index the star bit 8 in a slightly different poistion after each stroke, enhancing the cutting of chips.

As mentioned earlier, the apparatus in the figures may be modiied in many respects without varying from. the spirit or scope of the invention. It is possible to use various metals and alloys in the con-struction of the equipment illustrated, and it is possible to use the apparatus in combination with many conventional forms of drilling equipment such as rotary drill pipe, iiow tubing, surface rotary drive equipment, etc.

What is claimed is:

l. An apparatus for obtaining an uncontaminated sam ple from a subterranean formation immediately below a borehole which comprises a percussion-type bit, a reciprocating-type pneumatic motor adapted to drive said bit against the formation and to break the formation into small particles, first conduit means adapted to supply compressed air to said motor and to operate said motor, said rst conduit means also being adapted to supply a separate stream of air to the bottom of the borehole in the vicinity of the bit to lift said particles above the bit, a basket attached to said apparatus above said bit and adapted to collect the particles lifted above the bit, means to vent the exhaust air from the motor and from the bottom of the borehole to the surface of the earth, and means for sealing the collected particles within the basket.

2. An apparatus as defined in claim 1 including means for maintaining the pressure at the bottom of the borehole at a value at least equal to the formation pressure.

3. An apparatus as dened in claim 1 in which the sealing means is an inatable packer disposed within the entrance to the basket.

4. An apparatus as dened in claim 2 in which the pressure-maintaining means is an inflatable packer supported by the apparatus above the pneumatic motor and in the annular space between the apparatus and the wall of the borehole.

References Cited in the tile of this patent UNITED STATES PATENTS 1,250,103 Gihnan Dec. 11, 1917 1,753,339 Hencken Apr. 8, 1930 1,870,696 Taylor Aug. 9, 1932 1,881,258 Bayles Oct. 4, 1932 FOREIGN PATENTS 2,576 Australia Nov. l0, 1900 

1. AN APPARATUS FOR OBTAINING AN UNCONTAMINATED SAMPLE FROM A SUBTERRANEAN FORMATION IMMEDIATELY BELOW A 